An electrostatic capacitive sensing technology is a technology that uses a change in an electrostatic capacity to sense an external input, a change in external status, and presence of a substance. The electrostatic capacitive sensing technology is used in various fields. For example, the electrostatic capacitive sensing technology is used for a touch sensing apparatus that uses a change in the electrostatic capacity to sense a touch of a user, a level sensing apparatus that uses the change in the electrostatic capacity to sense a level of a substance, or a temperature sensing apparatus that uses the change in the electrostatic capacity to sense a change in a temperature. Hereinafter, the touch sensing apparatus will be described in detail. However, this is for a convenience of the description, but the description with respect to the touch sensing apparatus does not intend to exclude the applicability of the present invention to other fields.
The touch sensing apparatus receives an input of the user through a touch pad (or a touch screen or a touch key). If there is a touch of the user in a touch pad, an electrostatic capacity in the touch pad is increased (alternatively, the touch pad may be designed to decrease the electrostatic capacity in the touch pad if there is a touch of the user). If there is no touch, the electrostatic capacity in the touch pad refers to an electrostatic capacity that is formed between an electrode disposed in the touch pad and a ground. If there is a touch, the electrostatic capacity in the touch pad refers to an electrostatic capacity formed between an electrode disposed in the touch pad, a substance that is used to touch the touch pad (a finger of the user or stylus) and the ground. In other words, the touch sensing apparatus is an input apparatus that is manufactured based on a principle in that a substance used to touch has a higher electrostatic capacity than the air.
The touch sensing apparatus of the related art adopts a method that senses a touch using a sensing frequency. In other words, the touch sensing apparatus of the related art uses a method that generates a waveform having a frequency (hereinafter, referred to as a “sensing frequency”) corresponding to an electrostatic capacity in the touch pad, modulates the waveform into a clock, counts the clock, and uses a count value to sense the touch. However, there is a problem in that such a sensing frequency is vulnerable to a CS noise, an RS noise, and a radio noise. For example, due to a phenomenon that a sensing frequency follows a noise frequency, the sensing frequency does not exactly reflect an electrostatic capacity of the touch pad, which causes an error in determining a touch.
In order to solve the above-mentioned problem, engineers spend 70% of development time of a touch sensing apparatus in order to avoid the noise. Further, in order to avoid the noise of the sensing frequency, a method that uses a plurality of frequencies in a sensing section or a method that improves a sensing algorithm is suggested. However, this method has problems in that a cost of the touch sensing apparatus is increased and the structure of the touch sensing apparatus becomes complicated.